Improvements in methods for jointing units of concrete



March 1 l, 1958 E; J. VON HEIDENSTAM 2,825,957

IMPROVEMENTS IN METHODS FOR JOINTING UNITS OF CONCRETE Filed Nov. -4, 1953 FIG Jr N VEN TOR.

United States Patent IMPROVEMENTS IN METHODS FOR JOINTING UNITS OF CONCRETE Erik Johan von Heidenstam, Stockholm, Sweden Application November 4, 1953, Serial No. 390,222 Claims priority, application Sweden November 5, 1952 4 Claims. (Cl. 25-154) Heretofore, when assembling and joining separate, independent, prefabricated elements of concrete, the only method of pre-stressing the reinforcement irons in the joint was based upon the idea of pulling the concrete elements apart. This, however, widens the joints, and in many cases (for instance, when building vaults or cupolas of arched elements) it is impossible to pull the elements apart.

When factory-cast units are assembled in the building site, it is a well-known fact, that it is always the joints formed in the building sites, that cause inconveniences, and which are the weakest points in the finished structure. While the concrete of the units already has gone through its process of shrinking, the shrinkage remains within the joints, which more or less tend to open. Such joints easily become more water-permeable than the concrete units themselves, and furthermore the joint-s normally are weaker.

In order to avoid this undesirable action by the joints it was earlier often necessary to make certain types of structures in the form of monolithic castings, whereby difficulties arose with regard to the organization of the work, whereby joints might be dispensed with or reduced to a minimum. According to the invention such structures may instead be made by assembling factory-made units of moderate size, and thus standardization is attained, the accuracy of the performance is increased, the manufacture is rationalized, the consumption of material with regard to concrete as well as to reinforcement is reduced, and loads owing to own weight are reduced.

The present invention relates to a way of joining units of concrete or the like, which contain reinforcing iron (such as strap iron) cast into the concrete, said reinforcing iron projecting through the sides of the concrete units.

The invention also relates to means for carrying out the joining.

Great advantages are gained by the invention, particularly as the method can be applied in a great number of cases with regard to the assemblage of prefabricated concrete units. The invention can be-applied in the joining of units in the form of plain, single curved or double curved slabs, beams, etc.

While formerly, as far as such high-class factory-made, prestressed concreted units were concerned, it was necessary to join these in the building site in a manner that resulted in a plurality of joints disclosing different kinds of defects, it is possible according to the invention to assemble building units in a technically perfect manner by using factory-made prestressed units so that also the joints make a qualitatively equivalent part of a monolithic structure entirely prestessed.

According to the invention the reinforcement of the joint can be placed in its exact position and can be accurately prestressed. In connection with the joining it must be noted that the loss of reinforcement in the joints will be reduced to a minimum, no ineffective joining lengths are required.

In structures in which the reinforcement is not rectilinear, but bent or broken at least in certain points it is possible according to the invention to reduce the losses caused by the prestressing process considerably as compared with what is the case when reinforcing bars in holes are stressed after the concrete has solidified.

The new method of prestressing the joints renders it possible with economic advantage to make a plurality of types of large structures by using prestressed units of moderate size which are joined in the building site,"

prestressed longitudinally and/or transversely. In this way it is avoided in single or double curved structures (such as containers, silos, planked roofs, cupolas, etc.), to stretch reinforcing irons over or around the container etc. in the building site, as was earlier required, which reinforcement must afterwards be embedded or protected in some other way against corrosive substances. From this it can be understood, that it is possible in such cases, according to the invention to make prestressed structures with thinner and lighter walls than earlier, and which furthermore have the advantage, apart from the joints, to be made with the greater accuracy of the factory than that of the building site.

The view earlier held that prestressing according to the long line system or the fully bonded method is economic only with regard to concrete strings of great length is disregarded by the present invention, as the small or non-existing reinforcement losses in connection with the joining are economic, also when small units are concerned.

The invention will be hereinafter described reference being had to a number of figures, further characteristic features of the invention being set forth.

Figure 1 is a side view of two elements placed in positionto be jointed in accordance with the invention.

Figure 2 is a section along the line IIII in Fig. 1.

Figure 3 is a side sectional view of jointing irons in the form of thin pressedmetal plates.

Figure 4 is a side sectional view showing jointing irons pressed into each other.

Figure 5 is a side view of reinforcing iron joints.

Figure 6 is a section on the line VI-VI of Fig. 5.

Referring now to the Figs. 1 and 2 in the drawings the two separate, independent elements 1 of concrete have reinforcement rods 2.

The two prefabricated elements 1 are placed close to each other in the exact position that they shall have after the joining. They are held apart by blocks 17. Loops of the reinforcement irons 2 project outside the elements 1 and between adjacent loops jointing irons 18 and 19 are introduced which by means of atool hereinafter described are separated with a force the value of which is well-known, the reinforcement in the joint being tensionally prestressed to the desired degree. When the jointing irons 18, 19 assume the position in relation to each other corresponding to this, they are secured to each other and form a rigid unit. When concrete has been filled in the joint 5 and preferably has solidified, the support blocks 17 are removed, and

the interspace is filled with concrete, cement mortar or the like or is left unfilled. In order. to facilitate the removal of the support blocks, each preferably consists of several wedge-shaped units placed against each other. Due to the fact that the support blocks have been removed the concrete in the joint 5 will be compressionally prestressed to the desired extent, and the joint does not difier in this respect from that part of the finished structure constituted by the prestressed factory-cast concrete units 1.

Fig. 3 shows jointing irons 18, 19 in the form of thin, pressed plates, along the edges of which a support plate 23 is formed in which the reinforcement 2 rests. After the jointing irons have been pressed apart, they are welded together electrically.

Fig. 4 shows how two jointing irons 18, 19 can be pressed into each other to be interconnected to a rigid unit.

Figs. 5 and 6 show how the jointing irons 18, 19 to be pressed apart by the wedge 20 are formed in order to cause the stressing forces from the U-loops of the reinforcing irons 2 to be located in a plane close to and parallel to the plane in which the reinforcing irons otherwise are placed.

Figs. 79 illustrate the principle described above in connection with Figs. 5a and 6. in Figs. 7-9 the jointing irons 18, 19 consist of thin sheet metal corrugated to increase its rigidity. Slots are cut in the edges of the metal sheets 18, 19 to form tongues or tabs which are bent alternately in opposite directions to form supports for the reinforcing irons 2.

According to the invention it is possible to join units and form structures with plain, single curved or double curved surfaces.

According to the invention it is possible simultaneously to prestress the joints of a great portion of the finished structure, said portion comprising a plurality of concreteunits,, or to carry out the prestressing successively according as theassemblage proceeds.

In certain cases the reinforcing bars can be pressed apart after the concrete or other cementitious mass has been introduced into the joint, but while it is still plastic, at least under the action of vibration or some other treatment.

. Thus, it is possible according to the invention to assemble a construction, for example a cupola or roof of pre fabricated units, and to join the units successively while the assemblage is being carried out, so that a monolithic prestressed structure is attained.

Prefabricated prestressed units of a moderate size thus can be joined in the building site to the largest structures, the amount of concrete in the joints being relatively small, owing to which quick joining, for example by using a rapidly solidifying cement, is made possible for forming large surfaces. This is of" great importance with regard tov structures of different kinds, for example planked roofs, in such cases when the prefabricated units are joined in the building site, before the light vaulted girders are erected to their position on erected columns and/or walls. The girders also can be lifted by means of a fixing device and the last joining is carried out after the girders have been placed in position.

By using prefabricated units which are already contracted when assembled and joined according to the inventlon the shrinkage of the concrete which occurs in the casting of planked roofs in situ and is injurious in certain cases, and which has also led to collapse of the construction, is eliminated.

The invention renders it possible to reduce the quantity of concrete casting molds and scaffolding necessary on the building site. Instead movable cranes are used by means of which the units are assembled. Due to the fact that light structures are used the assemblage can be carried out in certain cases by using neither cranes nor scaffolds. This is for example the case as far as domes of moderate size are concerned.

In most cases it is preferable according to the invention to use reinforcement of the same type as that used in the production of string concrete (high test reinforcement). In certain cases, however, it may be preferred to provide the concrete units with projecting reinforcing bars of a material with marked elastic limit, U-shaped ends belonging together being stressed exactly to the elastic limit, the exact tension being known independently within certain limits of the magnitude of the deformation.

By prestressed joining is in this description meant joining of reinforcing irons belonging to adjacent concrete units in such a manner that a certain tension is effected within the joint.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

l. The method of jointing and interconnecting separate, independent, prefabricated elements of concrete or other cementitious material reinforced by irons permanently cast into the concrete and projecting outwards from said elements, comprising, placing the concrete elements in their final positions separated by supports in serted into the spaces between said elements, and with the projecting portions of said reinforcing irons located in the spaces between said elements, applying tensional force to the portions of said irons in said space so that said supports abut said elements and absorb the compression forces of reaction thereby applied to said elements by the tensioning of said irons, filling the space between said elements Withconcrete, leaving the concrete to solidify, and releasing said supports from supporting contact with said elements, thereby applying compressive force to the solidified concrete in said joints.

2. The method of permanently and rigidly interconnecting prefabricated separate units of concrete reinforced by irons permanently cast into the concrete to at least a portion of their length and protruding out of the elements, comprising, placing one element in position, placing the, next element at its final distance from the first element with the protruding portions of said irons extending into the space between said elements, inserting at least onerigid'support between said elements to support and keep them at their predetermined final distance from each other, said distance being the width of the joint to be made, coupling the protruding reinforcement irons in pairs, one from each element, in the interspace between the elements, tensioning the coupled reinforcement irons in relation to each other, while said support absorbs the compressive forces of reaction thus applied to said elements, filling the joint with mortar, leaving the mortar to solidify, and then removing said support, to cause the solidified mortar of said joint to have compressive force applied thereto.

3. The method of permanently and rigidly interconnecting prefabricated separate units of concrete reinforced by irons permanently cast into the concrete to at least a portion of their length and protruding out of the elements and with the protruding portions of said reinforcing irons located in the spaces between said elements, comprising, placing an element in position, placing the next element at its final distance from the other as determined by an interposed support, said distance being the width of the joint to be made, coupling the protruding reinforcement irons in pairs, one from each element, in the interspace between the elements, tensioning the reinforcement irons in relation to each other, while the support absorbs the compressive forces of reaction thus applied in the elements, fixing the reinforcement irons of a pair relative to each other by attaching them to insertions to keep them stressed, filling the joint with concrete, and removing said support after the concrete has solidified in the joint to apply compressive stress to the concrete of the joint enclosing the reinforcing irons.

4. The method of jointing and rigidly interconnecting independent, prefabricated elements of concrete reinforced by irons permanently cast into the concrete to a part of their length and protruding in U-shaped loops out of the elements, comprising, inserting at least one support into the space between the elements to keep a predetermined interspace between them equal to the width of the joint to be made, inserting jointing members into said loops in pairs, one from each element, while pressing them apart to apply tension to said irons, fixing the irons in their tensioned positions, filling concrete into the space be tween the elements, and removing the support, after the concrete has solidified to apply the compressive force of reaction to the concrete in said space.

References Cited in the file of this patent UNITED STATES PATENTS Thomas Jan. 28, 1941 

